Clock oscillators are devices which control the timing and operation of logic circuitry. The use of such devices is extremely widespread in consumer and industrial electronic products. A personal computer system, for example, may use several clock oscillators in the main processing unit as well as on add-in circuit boards and video graphics adapters, and in all of the peripheral devices such as printers, modems and networking equipment. In the telecommunication industry, clock oscillators are used in facsimile machines, cellular phones and radio transmission and receiver systems.
Clock oscillator devices are presently made by combining in a single package a frequency control device, such as a quartz crystal, and a hybrid circuit of resistors, capacitors and either transistors or an integrated circuit. The components are mounted on a thick film substrate or printed circuit board with the package being protected from the environment by a hermetically sealed metal can which also serves to reduce noise, that is, the unwanted electromagnetic and radio frequency emissions which oscillators often generate. These existing packages conform to DIP (dual in-line pin) standards and typically employ 8 or 14 pins.
With the continuing need for further miniaturization of electronic components, attempts have been made to produce more compact clock oscillator packages. Such units, however, continue to conform to DIP package standards and often do not incorporate passive components such as power supply filter capacitors. These components must therefore be added separately external to the clock oscillator package. Examples of such units are disclosed in U.S. Pat. No. 4,916,413 issued Apr. 10, 1990 to Nakayama et al.
Another drawback of existing resin-encapsulated clock oscillator devices is that as a result of the positions and orientations of the components on the lead frame relative to the placement and orientation of the resin injection gate, the transfer molding operation used to resin encapsulate the components tends to disturb the components and lead traces of the lead frame sometimes to the extent that delicate bonded connections are broken. Moreover, because of the rapid hardening rate of the epoxy resin that is typically employed, the resin does not always fill the entire cavity thereby often compromising the mechanical integrity of the unit and eventually exposing the encapsulated components and their connections to ambient environmental effects.